Embodiments of the subject matter disclosed herein generally relate to turbomachines, and more particularly, to devices and methods for improving rotordynamics in turbomachines.
Labyrinth seals are commonly used in order to minimize leakages from high pressure regions to low pressure regions in turbomachines such as pumps, centrifugal compressors, and turbines. Labyrinth seals include a number of grooves or teeth that form a tortuous path, or “labyrinth” between a stationary portion, or “stator,” and a rotating portion, or “rotor,” of the turbomachine. Labyrinth seals may be statoric, in which the teeth are formed on the stator, or rotoric, in which the teeth are formed on the rotor. The grooves or teeth of the labyrinth seal and opposing surface impede the flow of fluids from the high pressure region to the low pressure region through the labyrinth seal. However, a space or clearance is necessary between the labyrinth grooves or teeth and an opposing surface to allow rotation of the rotor. Thus, although labyrinth seals impede fluid flow, the clearance allows highly pressurized fluid from the high pressure region to leak through the clearance to the low pressure region due to a pressure differential across the labyrinth seal. Labyrinth seals in general are designed to contain this leakage.
Leakage flow through the labyrinth seal may be reduced by decreasing the clearance. To this end, abradable labyrinth seals have been developed. Abradable labyrinth seals are rotoric labyrinth seals in which a statoric portion that opposes the rotoric teeth is formed of an abradable material. Clearances in abradable labyrinth seals may be made very small because when the rotoric teeth rub against the abradable stator such as occurs, for example, due to rotoric vibration during transient conditions, the rotoric teeth cut into the abradable material of the stator, thereby increasing the clearance. Abradable labyrinth seals are practically not applicable in high pressure centrifugal compressors because of their high destabilizing effects. The seal contribution to instability is related to the possibility to create a gas annulus, along the circumferential direction, rotating together with the rotoric part. Those small gaps favorite to keep the gas trapped into the circumferential path with higher destabilizing effects.
Although small clearances in both statoric and rotoric labyrinth seals can reduce leakage, they also negatively influence rotor stability due to inlet swirl at the entrance to the labyrinth seal and circumferential flow created inside the labyrinth seal by centrifugal force due to rotation. In an attempt to improve rotor stability, labyrinth seals in turbomachines have been modified with swirl brakes or equipped with shunt holes. For example, statoric impeller eye labyrinths are usually modified to include swirl brakes and balance drums are usually equipped with shunt holes. However, these devices can be difficult to implement and introduce additional costs in the manufacture and design phases of the turbomachines. Furthermore, no devices are currently available to stabilize rotoric labyrinth seals on impeller eyes.
Accordingly, it would be desirable to provide systems and methods for improving rotordynamics in turbomachines simply and cost-effectively.
In particular, from a mechanical point of view, in high pressure centrifugal compressors, the presence of high differential pressures requires mechanically stiff seals with high strength capabilities. For these reasons labyrinth seals in centrifugal compressors are machined starting from an aluminum or steel ring instead of assembling small annular ribs to create a single chamber as it is done in the turbines. At the same time, the presence of gas contaminants typical of oil and gas industry as H2S, CO2 and others together with the need of employing high reliable and referenced solutions, leads to the use of well-known materials with high mechanical properties both in terms of stress strength and corrosion resistance (typically aluminum and steels).
The present invention aims at improving the actual design of labyrinth seals in high pressure centrifugal compressors and at giving a new solution solving both the need of stability and sealing capabilities together with the use of well-known materials.